avoid some connection types (don't prefer zerotier)

I have a syncthing connection between 2 nodes that are also on a shared zerotier network. This appears like a special ethernet device with a network that tunnels between sites.

Syncthing quickly discovers that the 2 nodes can talk via zerotier and makes connections like this: [fe80::b066:d7ff:fe21:d366%ztrf27jonu]:47412 (the tooltip says this is a tcp_server connection)

This connection works fine and so Syncthing is correct to use it, however, since that tunnel is encrypted it is slower than a direct TCP connection over the internet.

Is there a way to specify that some network interfaces should be preferred over others?

If not can I blacklist that zerotier network device?

There is an advanced setting for each device called allowed networks, so you can specify a CIDR you prefer syncthing to use.

Otherwise I don’t think we’re smart enough to prioritize between addresses of the same protocol. If we were, link local ipv6 would be at the very top of the list though as that’s likely to be the most local and hence fastest.